1. FIELD OF THE INVENTION
The present invention relates to an electrochemical polarographic gas analyzer and, more particularly, to a gaseous phase oxygen analyzer and to methods of using the analyzer to determine oxygen in the presence of other gases having polarographic reduction potentials near to that of oxygen.
2. DESCRIPTION OF THE PRIOR ART
Electrochemical gas analyzers have been available for several years which measure oxygen content of a gas or fluid by diffusing oxygen through a semi-permeable membrane into an electrolyte layer adjacent the cathode. A polarographic voltage is applied relative to an anode spaced therefrom and the resultant depolarizing current is measured by means of an external circuit.
The linearity and accuracy of response and the magnitude of the electrical signal are affected by the spacing of the membrane from the cathode and by the cathode response characteristics. A further limitation in the life of the electrochemical cell is the electrolyte. Typical electrolytes for polarographic sensors are aqueous solutions of alkali metal halides which tend to dry out as the cell is used, requiring the cell to be discarded unless it is of the type in which the electrolyte may be replaced. Opening the cell to replace electrolyte is a difficult operation, especially in the field, and cells with replaceable electrolyte require purchase and storage of the electrolyte and replacement membranes.
One application in which oxygen sensing electrochemical cells have been utilized is in the determination of the oxygen content of clinical, anesthetic nitrous oxide containing gas mixtures. One type of cell utilized currently is a galvanic cell. However, during operating the anode employed, which reduces oxygen at the cathode, will also reduce nitrous oxide to nitrogen at its surface. The nitrogen produced at the anode collects within the sealed electrochemical cell, causing lifting of the membrane, which changes the thickness of the electrolyte film and therefore the diffusion path from membrane to cathode causing incorrect readings and may eventually lead to rupture of the gas permeable membrane.